An attempt to fix oid overflow in regclass

[elpaso]

QGIS was using int to store oids, but oids are 4 byte unsigned ints.

This is an attempt to partially fix #30041

[elpaso]

@jef-n what do you think?

[backporting]

The backport to release-3_4 failed:

Commits ["ad8c5a6d98dfe2cd206ec5157fc8778af998980d","c90583c0dbaea80ca3b4c14dfd4d9a305d7fc733","c94310df56119d61089249ee7bbc5ad188a6096c"] could not be cherry-picked on top of release-3_4

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub.
git fetch
# Create new working tree.
git worktree add .worktrees/backport release-3_4
# Navigate to the new directory.
cd .worktrees/backport
# Cherry-pick all the commits of this pull request and resolve the likely conflicts.
git cherry-pick ad8c5a6d98dfe2cd206ec5157fc8778af998980d c90583c0dbaea80ca3b4c14dfd4d9a305d7fc733 c94310df56119d61089249ee7bbc5ad188a6096c
# Create a new branch with these backported commits.
git checkout -b backport-30184-to-release-3_4
# Push it to GitHub.
git push --set-upstream origin backport-30184-to-release-3_4
# Go back to the original working tree.
cd ../..
# Delete the working tree.
git worktree remove .worktrees/backport

Then, create a pull request where the base branch is release-3_4 and the compare/head branch is backport-30184-to-release-3_4.